Ordered mesoporous ceramics stable up to 1500 degrees C from diblock copolymer mesophases

In the present study, a poly(isoprene-block-dimethylamino ethyl methacrylate) diblock copolymer (PI-b-PDMAEMA) is used to structure-direct a polysilazane pre-ceramic polymer, commercially known as Ceraset. To the polymer was added a 2-fold excess in weight of the silazane oligomer (Ceraset). The resulting composite was cast into films, and after cooperative self-assembly of block copolymer and Ceraset, the structure was permanently set in the hexagonal columnar morphology, as evidenced by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Cross-linking of the silazane oligomer was achieved with a radical initiator at 120 degrees C. Upon heating of the composite to 1500 degrees C under nitrogen, the structure is preserved and a mesoporous ceramic material is obtained, as demonstrated by SAXS and TEM. The pores are open and accessible, as evidenced by nitrogen sorption/desorption measurements indicating a surface area of about 51 m2 g-1 and a pore diameter of 13 nm, consistent with TEM analysis. These results suggest that the use of block copolymer mesophases may provide a simple, easily controlled pathway for the preparation of various high-temperature ceramic mesostructures.     

Direct Access to Isotopically Labeled Aliphatic Ketones Mediated by Nickel(I) Activation

An extensive range of functionalized aliphatic ketones with good functional‐group tolerance has been prepared by a Ni^I‐promoted coupling of either primary or secondary alkyl iodides with NN₂ pincer Ni^II‐acyl complexes. The latter were easily accessed from the corresponding Ni^II‐alkyl complexes with stoichiometric CO. This Ni‐mediated carbonylative coupling is adaptable to late‐stage carbon isotope labeling, as illustrated by the preparation of isotopically labelled pharmaceuticals. Preliminary investigations suggest the intermediacy of carbon‐centered radicals.     

Stable N,N’-Diarylated Dihydrodiazaacene Radical Cations

Three stable N,N’-diarylated dihydroazaacene radical cations were prepared by oxidation of neutral N,N’-diarylated dihydroazaacenes synthesized via palladium-catalyzed Buchwald-Hartwig aminations of aryl iodides with N,N’-dihydroazaacenes. Both neutral as well as oxidized species were investigated via UV-vis spectroscopy, single crystal analysis, and DFT calculations. All the radical cations are surprisingly stable—their absorption spectra in dichloromethane remain unchanged in ambient conditions for at least 24 hours.     

Porous Membranes Built Up from Hydrophilic Poly(ionic liquid)s

Porous polymer membranes made via electrostatic complexation are fabricated from a water‐soluble poly(ionic liquid) (PIL) for the first time. The porous structure is formed as a consequence of simultaneous phase separation of the PIL and ionic complexation with an acid, which occurred in a basic solution of a nonsolvent for the PIL. These membranes have a stimuli‐responsive porosity, with open and closed pores in isopropanol and in water, respectively. This property is quantitatively demonstrated in filtration experiments, where water is passing much slower through the membranes than isopropanol.

     

Interlaboratory comparison of size and surface charge measurements on nanoparticles prior to biological impact assessment

The International Alliance for NanoEHS Harmonization (IANH) organises interlaboratory comparisons of methods used to study the potential biological impacts of nanomaterials. The aim of IANH is to identify and reduce or remove sources of variability and irreproducibility in existing protocols. Here, we present results of the first IANH round robin studies into methods to assess the size and surface charge of suspended nanoparticles. The test materials used (suspensions of gold, silica, polystyrene, and ceria nanoparticles, with [primary] particles sizes between 10?nm and 80?nm) were first analysed in repeatability conditions to assess the possible contribution of between-sample heterogeneity to the between-laboratory variability. Reproducibility of the selected methods was investigated in an interlaboratory comparison between ten different laboratories in the USA and Europe. Robust statistical analysis was used to evaluate within- and between-laboratory variability. It is shown that, if detailed shipping, measurement, and reporting protocols are followed, measurement of the hydrodynamic particle diameter of nanoparticles in predispersed monomodal suspensions using the dynamic light scattering method is reproducible. On the other hand, measurements of more polydisperse suspensions of nanoparticle aggregates or agglomerates were not reproducible between laboratories. Ultrasonication, which is commonly used to prepare dispersions before cell exposures, was observed to further increase variability. The variability of the zeta potential values, which were also measured, indicates the need to define better surface charge test protocols and to identify sources of variability.     

Comparison of the photosensitivity and bacterial toxicity of spherical and tubular fullerenes of variable aggregate size

Nanomaterials such as fullerene C₆₀, carbon nanotubes (CNTs), and other fullerenes show unique electrical, chemical, mechanical, and thermal properties that are not well understood in the context of the environmental behavior of this class of carbon-based materials. In this study, aqueous suspensions of three fullerenes nanoparticles, C₆₀, single-wall (SW) and multi-wall (MW) CNTs were prepared by sonication and tested for reactive oxygen species (ROS) production and inactivation of Vibrio fischeri, a gram-negative rod-shaped bacterium, under ultraviolet (UV)-A irradiation. We show that ROS production and microbial inactivation increases as colloidal aggregates of C₆₀, SWCNT, and MWCNT are fractionated to enrich with smaller aggregates by progressive membrane filtration. As the quantity and influence of these more reactive fractions of the suspension may increase with time and/or as the result of fractionation processes in the laboratory or the environment, experiments evaluating photo-reactivity and toxicity endpoints must take into account the evolution and heterogeneity of nanoparticle aggregates in water.     

A risk forecasting process for nanostructured materials, and nanomanufacturing

Nanomaterials exhibit novel properties that enable new applications ranging from molecular electronics to energy production. Proactive consideration of the potential impacts on human health and the environment resulting from nanomaterial production and use requires methods for forecasting risk associated with of these novel materials. However, the potential variety of nanomaterials is virtually infinite and a case-by-case analysis of the risks these materials may pose is not possible. The challenge of forecasting risk for a broad number of materials is further complicated by large degrees of uncertainty concerning production amounts, the characteristics and uses of these materials, exposure pathways, and a scarcity of data concerning the relationship between nanomaterial characteristics and their effects on organisms and ecosystems. A traditional risk assessment on nanomaterials is therefore not possible at this time. In its place, an evolving process is needed for analyzing the risks associated with emerging nanomaterials-related industries.In this communication, we propose that such a process should include the following six key features: (1) the ability to generate forecasts and associated levels of uncertainty for questions of immediate concern; (2) a consideration of all pertinent sources of nanomaterials; (3) an inclusive consideration of the impacts of activities stemming from nanomaterial use and production that extends beyond the boundaries of toxicology and include full life cycle impacts; (4) the ability to adapt and update risk forecasts as new information becomes available; (5) feedback to improve information gathering; and (6) feedback to improve nanomaterial design. Feature #6 implies that the potential risks of nanomaterials must ultimately be determined as a function of fundamental, quantifiable properties of nanomaterials, so that when these properties are observed in a new material, they can be recognized as indicators of risk. Thus, the required risk assessment process for nanomaterials addresses needs that span from urgent, short-term questions dealing with nanomaterials currently in commerce, to longer-term issues that will require basic research and advances in theory. In the following sections we outline issues surrounding each of these six features and discuss.     

Investigation of the electrode effects in mixed potential type ammonia exhaust gas sensors

Mixed potential ammonia exhaust gas sensors provide a high capability for applications in harsh environments when appropriate means are conducted to stabilize the electrodes catalytic activity. The discussed sensor utilizes oxygen ion conducting yttria stabilized zirconia and gold electrodes, one of which is covered with an SCR active film to establish ammonia sensitivity and selectivity. The used SCR catalyst is well-known and developed especially for ammonia SCR exhaust gas aftertreatment systems. Electrochemical half-cell measurements vs. a Pt reference indicate that both electrode configurations are electro catalytically active for ammonia oxidation, but the activity is more pronounced at the additional SCR catalyst layer. The results of the half-cell tests including ammonia dependent voltage and oxygen interference agree very well with the performance of the ammonia sensor device. The behavior of the catalyst electrode cover is characterized separately by activity measurements of powders. The sensing mechanism combines electrochemical reactions at the three phase boundary and chemical reactions at the catalyst material.     

Aggregation and Deposition Characteristics of Fullerene Nanoparticles in Aqueous Systems

The propensity of n-C₆₀ to aggregate and deposit will play a key role in determining its longevity in aquatic systems, and therefore the potential exposure and risk presented by these colloids. We consider the origin of n-C₆₀ stability and compare the aggregation and deposition characteristics of n-C₆₀ under conditions of variable ionic strength using an indifferent electrolyte. Relatively weak electrolyte solutions (0.001 M) were observed to destabilize suspensions of n-C₆₀ resulting in the formation of settleable aggregates. This behavior supports the hypothesis that the stabilizing mechanism for n-C₆₀ clusters is electrostatic in origin. Similarly, the deposition of n-C₆₀ in porous media increased as ionic strength increased. These observations suggest that under some conditions present in natural aquatic systems, these materials may have limited mobility as they form large aggregates that may settle out of suspension or deposit on surfaces. These phenomena may, at least partially, offset any risk presented by n-C₆₀ toxicity due to a reduced potential for exposure.